Forgive me if I have failed to find a thread on this, I did try.

Do we know how the XK calculates the range in miles based on current fuel level?

On a Land Rover forum this question was asked and amazingly the guy that wrote the program turned up. It was a little odd but made sense. It wasn't simply based on current fuel in gallons and the current average mpg, it was biased towards the historic average plus the current trip.

 

Recent history + current usage is my understanding.

Miles to empty will increase substantially when you are going cross country and refill the tank once or twice in quick succession after a few hundred miles of all highway / high mpg driving.


Z

 

I suspect you are right but how recent is recent?

I had to smile when you said 'high mpg driving'. My other car is a Honda diesel that happily returns 70+ UK mpg on the highway.

 

There is also a safety margin when the displayed range drops to zero as I was very relieved to discover on a dark Winter night in North Yorkshire on the A1(M).

Graham

 

I am happier with the XKR’s begrudging 22 mpg than I would be with a happy Honda’s 70+ mpg.


Z

PS recent is very recent. Once one or two tankfuls of gasoline has gone thru the car at highway mpg, then the miles to empty is showing that rate of consumption. The previous & much lower city driving mpg has obviously been out of the calculations.

Very easy to verify by dividing the miles-to-empty displayed number by the number of gallons of gas left in the tank. That number will always be very close to your current average mpg if you have been driving at a steady rate.

 

Sadly I don't do many longer drives in the XK - UK fuel is a lot more expensive than in the US and your roads are long and relaxed compared to ours - so I can't really test your mathematics.

My wife never quite believes how far you can travel in a day on your roads, 400 miles is easy and pretty relaxed if you're not in a city. In the UK 400 miles will be quite tiring even on motorways as our traffic density is much greater. We have had a truly wonderful times driving in the South West, mainly CA, AZ and NV. But for Covid we'd have done bits of Utah and New Mexico. Our son lives in CA and it's been two years sine we have seen him.

I'll be honest and say I didn't think I'd like the US but I fell in love very quickly although I wouldn't want to be poor in California for sure. I thought I'd struggle with the driving but your roads (outside the cities) are empty and good and you just roll along and take in the scenery. I have totally fallen in love with deserts. Yours is a wonderful country with wonderful people.

Yeah the Honda is a different dive and well suited to the UK. On a visit home my son hired a bigger car and regretted it as he hadn't driven that much on UK roads which the Jag handles well enough but a larger German saloon isn't so easy on real country roads. The fuel cost hurt him badly as well.

I can go off on tangents

 

From memory, the tank is about 20 gallons. Even going down to a range of "zero" miles, I have not been able to put more than 18 gallons during a refill. Not to say the fuel pump would be able to get to the last drop of course. Also, when the range goes down to double digits, it seems be be influenced by the car's pitch, with reduced range when the nose is down.

 

some cars use the fuel injector pulse count as a very accurate contribution to the formula. Over time with a consistent count this would provide the most accurate result for usage, MPG and ultimately range.

 

I've found that the “fuel-used” display is very accurate when needing to determine how much is actually Left in the tank. The “miles-to-empty” has too many variables to be a reliable indicator of how much fuel is left on board.

Z


PS my 2002 MY tank holds 20 US gallons . Not sure if that holds true across all model years.

PPS to keep the fuel pumps as cool as possible it’s prudent to not let the fuel level drop below 1/4 tankful

 

Remembering of course that a US gallon is only 3.78 litres and a UK gallon 4.546 litres so the US is 83% of a UK gallon.
I would also suggest that as the speedo on a UK car is reading low (76 on the clock is true 70) that the milometer is also low.

 

Presumably our cars do something similar to work out the instant MPG - you wouldn't even need to go as basic as use the injector pulse counts as the computer knows what fuel value it has calculated it wants in the first place. That along with RPM and gear selected/road speed would be a very simple formula to work out instant MPG.